Such a respiration system is known through the instructions for use for the “Zeus Infinity Empowered” system of Dräger Medical GmbH. Such respiration systems with a rebreathing line are designed, as a rule, such that based on a patient port or Y-piece, via which a patient is connected to the respiration system, an inspiration branch and an expiration branch are provided, whose ends located away from the patient port are connected to one another via the rebreathing line, which extends in the housing of the respiration system. A reservoir, such as a manual breathing bag for receiving breathing gas, a CO2 absorber and a respiration drive, preferably in the form of a radial compressor, with which breathing gas can be delivered into the inspiration branch, are provided, as a rule, in the rebreathing line.
In addition, nonreturn valves, which prevent breathing gas expired by the patient from leaving the inspiration branch and breathing from being able to be pressed from the rebreathing line directly in the expiration branch, are provided in the respective inspiration and expiration branches. Finally, a control valve or positive end-expiratory pressure (PEEP) valve, which can be opened or closed by a control, is arranged close to the connection between the expiration branch and the rebreathing line.
The control valve is closed during the inspiration phase in order to prevent breathing gas from being pressed directly again into the rebreathing line by the respiration drive instead of being pressed into the patient port. However, the control valve is opened during the expiration phase, so that the breathing gas discharged from the patient port can flow back from the expiration branch into the rebreathing line, and this breathing gas first enters the reservoir, i.e., usually the manual breathing bag.
Breathing gas is thus drawn during normal respiration operation at first during the inspiration phase by means of the respiration drive from the reservoir and returned to the patient port via the inspiration branch, and the control valve is closed during this phase. The control valve is opened during the expiration phase, and the expired gas returns again into the reservoir.
However, the problem may arise now that the reservoir or the manual breathing bag has too small a volume. Part of the gas arriving from the patient port is discharged now via a gaseous anesthetic escape valve (hereinafter called “NGF valve”) provided in the rebreathing line. However, the consequence of this is that an insufficient quantity of gas will be present in the system for the next inspiration phase and this gas must be compensated by feeding fresh gases. The respiration system cannot now be operated in the manner actually intended, in which latter case only a very small quantity of expensive gases must be fed anew.